Image comparison methods and equipment are widely used in manufacturing, testing, surveillance and many other applications. Current techniques of image comparison include image subtraction, color overlay and image flashing or alternating. Image subtraction algebraically combines the magnitude of each point or pixel of the reference image and test image so that like parts cancel and only differences remain. In the color overlay approach, each image is filtered with a different color so that differences appear in one or the other color and like parts appear as a blend of both colors. In image flashing, first one and then the other image is flashed on a screen: like parts remain steady; differences blink. However, these methods have a number of shortcomings and may fail or give poor results because of image-to-image misregistration and differences in overall intensity levels of the two images.